Signal communication for circuit with floating ground

Abstract

An electronic device includes a first circuit having a first ground that receives first and second control signals. A third control signal is produced by a second circuit. The second circuit uses a second ground, and the first ground floats with respect to the second ground. The first circuit determines a value corresponding to a value of a third control signal using a difference between a value of the first control signal and a value of the second control signal, the value of a third control signal being a value relative to the second ground. The first circuit controls a value of an output signal of the first circuit according to the value corresponding to the value of a third control signal.

What is claimed is: 
     
       1. An electronic device comprising:
 a first circuit having a first ground and including a difference circuit and a controller circuit, the first circuit configured to:
 receive a first control signal, 
 receive a second control signal, 
 determine, using the difference circuit, a value corresponding to a value of a third control signal using a difference between a value of the first control signal and a value of the second control signal; and 
 control, using the controller circuit, a value of an output signal of the first circuit according to the value corresponding to the value of a third control signal; 
 
 wherein the third control signal is produced by a second circuit having a second ground, 
 wherein the value of the third control signal is a value relative to the second ground, 
 wherein the first control signal corresponds to a voltage difference between the second ground and the first ground, 
 wherein the second control signal corresponds to a voltage difference between the third control signal and the first ground, and 
 wherein the first ground floats relative to the second ground. 
 
     
     
       2. The electronic device of  claim 1 , wherein a value of the first control signal corresponds to a difference between the first ground and the second ground. 
     
     
       3. The electronic device of  claim 1 ,
 wherein the controller circuit includes a Switch Mode Power Supply (SMPS) controller; and 
 wherein the output signal is a gate signal to control a switching device of a SMPS. 
 
     
     
       4. The electronic device of  claim 1 , further comprising:
 a first voltage divider configured to produce the first control signal using the second ground and the first ground; and 
 a second voltage divider configured to produce the second control signal using the third control signal and the first ground. 
 
     
     
       5. The electronic device of  claim 1 , wherein the first circuit is further configured to:
 produce, using the controller circuit, a detection signal indicating whether the value of the third control signal can be reliably determined using the difference between the value of the first control signal and the value of the second control signal; 
 determine the value corresponding to the value of the third control signal using a difference between the value of the first control signal and the value of the second control signal when the detection signal indicates that the value of the third control signal can be reliably determined using the difference between the value of the first control signal and the value of the second control signal; and 
 determine the value corresponding to the value of a third control signal using a previously sampled value of the difference between the value of the first control signal and the value of the second control signal when the detection signal does not indicate that the value of the third control signal can be reliably determined using the difference between the value of the first control signal and the value of the second control signal. 
 
     
     
       6. The electronic device of  claim 5 ,
 wherein the controller circuit includes a Switch Mode Power Supply (SMPS) controller capable of operating in a Discontinuous Conduction Mode (DCM), the SMPS controller configured to:
 receive a current sense signal, 
 produce, using the current sense signal and the value of the third control signal, the output signal, and 
 produce a blanking signal to prevent the output signal from being spuriously asserted by ringing on the current sense signal, and 
 
 wherein the detection signal is produced using the blanking signal. 
 
     
     
       7. An electronic device comprising:
 a first circuit having a first ground, the first circuit including:
 a Switch Mode Power Supply (SMPS) controller having a current sense input, a dimming voltage input, and a gate control output, the SMPS controller to control the gate control output according to values of the current sense input and values of the dimming voltage input, and 
 a differential amplifier having first and second differential inputs and an amplifier output, the differential amplifier to receive a first control signal on the first differential input, receive a second control signal on the second differential input, and produce the amplifier output according to a difference between the first and second differential inputs, 
 
 wherein the amplifier output is coupled to the dimming voltage input, 
 wherein the first control signal is produced using a voltage divider coupled between the first ground and a second ground, 
 wherein the second control signal is produced using a voltage divider coupled between the first ground and a third control signal, 
 wherein the third control signal is produced by a second circuit, the second circuit having the second ground, and 
 wherein the first ground floats relative to the second ground. 
 
     
     
       8. The electronic device of  claim 7 , wherein a value of the dimming voltage input relative to the first ground corresponds to a value of the third control signal relative to the second ground. 
     
     
       9. The electronic device of  claim 7 , where the first circuit further comprised: a sample-and-hold (S/H) circuit coupled between the amplifier output and the dimming voltage input, wherein the S/H circuit provides a value of the amplifier output to the dimming voltage input when a detect signal has a first value, and provides a previously sampled value of the amplifier output to the dimming voltage input when the detect signal has a second value. 
     
     
       10. The electronic device of  claim 9 , wherein the value of the detect signal is determined according to a blanking interval of the SMPS controller. 
     
     
       11. The electronic device of  claim 7 , further comprising a switching device, the switching device having a control terminal coupled to the gate control output, a first conduction terminal coupled to the first ground, and a second conduction terminal coupled to an energy-storage inductor. 
     
     
       12. A method of communicating a signal between two circuits, the method comprising:
 receiving, by a first circuit, a first control signal; 
 receiving, by the first circuit, a second control signal; 
 determining, by the first circuit, a control value using a value of the first control signal and a value of the second signal; and 
 controlling, by the first circuit, an output signal of the first circuit according to the control value, 
 wherein the control value corresponds to a value of a third control signal, 
 wherein the third control signal is generated by a second circuit, 
 wherein the first circuit uses a first ground, 
 wherein the second circuit uses a second ground, 
 wherein the value of the second control signal corresponds to a voltage difference between the third control signal and the first ground, and 
 wherein the first ground floats with respect to the second ground. 
 
     
     
       13. The method of  claim 12 , further comprising determining, by the first circuit, the control value by determining a difference between the value of the first control signal and the value of the second signal. 
     
     
       14. The method of  claim 12 , wherein the value of the first control signal corresponds to a voltage difference between the second ground and the first ground. 
     
     
       15. The method of  claim 12 ,
 wherein the first control signal is produced using a voltage divider, the voltage divider being coupled to the second ground and the first ground, and 
 wherein the second control signal is produced using a voltage divider, the voltage divider being coupled to the third control signal and the first ground. 
 
     
     
       16. The method of  claim 12 , wherein the first circuit comprises a Switch Mode Power Supply (SMPS) control circuit. 
     
     
       17. The method of  claim 12 , further comprising:
 determining, by the first circuit, a blanking signal indicating that the control signal should not be asserted; 
 determining, by the first circuit, a detection signal according to the blanking signal; 
 determining, by the first circuit, the control value using a present value of the first control signal and a present value of the second signal when the detection signal is asserted; and 
 determining, by the first circuit, the control value using a past value of the first control signal and a past value of the second signal when the detection signal is de-asserted. 
 
     
     
       18. The method of  claim 12 , further comprising:
 receiving, by the first circuit, a current sense signal corresponding to a current flowing through an inductor; and 
 controlling, by the first circuit, the output signal of the first circuit according to the control value and a value of the current sense signal.